Contax IIIa color dial - slow speeds not consistent

I got a Contax IIIa color dial, and the slow speeds (1s, 1/2, 1/5, 1/10) are not consistent. I have not done properly shutter speed testing yet, but here are the symptoms.

- Often it seems the slow speed retard section is not engaged at all, and 1s feels like 1/250s
- Once in a while the slow speed retard section do engage, and the slow speeds seems about right

Have anyone experienced something similar with Contax IIIa?
If yes, is it something that can be fixed relatively easily by yourself? or should I leave it to the professionals?

It sounds like the slow speed mechanism is sticking and not resetting after use, the shutter will then run down at the slowest unretarded speed (I thought this was 1/50th)
It sounds like it could to with a little cleaning and minor lubrication.

Youtube Video of Contax IIa slow speed servicing by Mikeo62

As shown the slow speed mechanism on the Contax IIa/IIIa is directly under the top cover, in case of the IIIa it is covered by the light meter unit which requires a few more screws to remove .
It is a relatively easy fix, but it really depends on how confident you are with camera repair.

@Mr Flibble thank you for the pointers. I will check the video out the decide what to do next.